Sen. John McCain, R-Ariz., the ranking Republican on the Senate Armed Services Committee (r.) joined by committee chairman, Sen. Carl Levin, D-Mich., questions Defense Secretary Leon Panetta on the crisis in Syria, on March 7, on Capitol Hill in Washington.

The question of how much leading the world’s top military power should do in conflicts – and how much force it should deploy, and when – is certain to figure prominently in the November presidential election as well.

This year, Republicans – among them, three of the party’s presidential aspirants – are attacking the president’s preference so far for diplomacy in dealing with Iran and its nuclear program. On Tuesday, Senate minority leader Mitch McConnell called for Congress to authorize the use of force in Iran.

Mr. Obama used a televised press conference Tuesday to punch back at his political rivals, saying how disturbed he has become by the “casualness” with which “these folks [who] don’t have a lot of responsibilities” are “beating the drums of war.”

But it was on Syria that the president came closer to defining his vision of when America should and shouldn’t lead the world in the use of force to address a conflict.

Obama conceded that the situation unfolding in Syria, where a “dictator” is slaughtering his own people, is “heartbreaking and outrageous.” But he added, “On the other hand, for us to take military action unilaterally, as some have suggested, or to think that somehow there is some simple solution, is a mistake.”

It was a line that may very well resurface in some presidential debate on US foreign policy and American leadership come October.

Obama contrasted Syria with last year’s Libya intervention, which he said was made possible by a united international community working after United Nations Security Council authorization.

“What happened in Libya was we mobilized the international community, had a ... Security Council mandate, had the full cooperation of the region, Arab states, and we knew that we could execute very effectively in a relatively short period of time,” he said. “[Syria] is a much more complicated situation.”

In his Senate testimony Wednesday, Secretary Panetta expounded on the administration’s cautious side when it comes to military intervention.

While allowing that Syria’s humanitarian crisis is “terrible,” he said, “What doesn’t make sense is to take unilateral action right now.” Before advising the president to deploy military forces, he added, “I’ve got to make very sure we know what the mission is [and] achieving that mission at what price.”

But the administration does have its more interventionist side – led by its generally more hawkish secretary of State, Hillary Rodham Clinton. And Obama has shown that he can heed that section of his advisers, as he did on Libya.

Last year in highest-level national-security debates on the Libya crisis, then-Defense Secretary Robert Gates took a cautious approach to intervention with questions very much like those Panetta presented to Senator McCain on Wednesday: What’s the mission, what’s the exit strategy, what are the risks?

Obama ended up siding with pro-interventionist Secretary Clinton, but with the United States playing an unusual, largely subordinate role in the NATO campaign, which resulted in the critics’ “leading from behind” description.

The president also heeded his cabinet’s interventionists in October, when he unilaterally dispatched 100 US troops to Uganda to help in the battle against the horrifically violent Lord’s Resistance Army and its leader, Joseph Kony.

Obama has also shown a willingness to use the military means at his disposal in much riskier and more diplomatically charged situations when the benefits appear to outweigh potential costs – and especially when the intervention would means no, or almost no, boots on the ground. The use of unmanned drones in places like Pakistan and Yemen has jumped under Obama, as has deployment of special forces.